1. Field of the Invention:
This invention relates to by-pass circuitry for use with electro-receptive devices. More particulary the invention is an automatic by-pass switching device for use with series connected illuminants, specifically, neon sign lamps and the relatively high voltages associated therewith. The invention automatically shunts around a neon lamp at the time the lamp burns out, in order to provided an alternative circuit to allow continued operation of the remaining lamps in the series circuit.
2. Description of the prior art:
Series connected lamps have been in wide use for many years. A well known problem associated with series circuited lighting is that if one lamp becomes inoperative, the entire circuit is interrupted and the remaining lamps in the circuit cease to function until the defective lamp is replaced and the circuit is again completed. Under the condition of all the lamps being inoperable due to one or more defective lamps, it is difficult and sometimes dangerous to ascertain which is the defective lamp since all the lamps are inoperative. It is not uncommon for a technician to receive a hazardous shock during testing for the defective lamp since most testing procedures are most readily performed with the power on. Also, when a series circuited neon lamp arrangement ceases to function due to one or more defective lamps, the transformer continues stepping the primary voltage to a higher secondary voltage with typical neon transformers having open circuit transformer voltages of about 12,000 volts, whereas operating voltages of the same transformer with functioning lamps will typically be around 6,500 volts. 12,000 volts will arc much further than 6,500 volts, and in the description of my invention, it will be shown how I have taken advantage of the greater arcing distance of the higher voltage of the open circuit transformer.
Over the years, several devices and circuits have been invented to automatically by-pass defective lamps in series lighting circuits to allow the remaining lamps to continue burning, making it simple and safe to locate the defective lamp. However, for one reason or another, few if any of such by-pass devices and circuits are currently used in the U.S. for neon lighting, and none appear to be as feasible or structured the same as my by-pass switching device.
A patent issued to A. J. Holt on Apr. 27, 1886, U.S. Pat. No. 340,717 teaches a "multiple series system of electrical distribution" which includes the teaching of an automatic cut-out or shunt mechanism which uses an armature with an electromagnet to shunt around one or more defective lamps.
A patent issued to William C. Fleck on Feb. 23, 1988, U.S. Pat. No. 4,727,449 teaches a "filament bypass circuit" for use with a string of lamps connected in series. Each lamp is provided with a shunt circuit consisting of a series circuit of a diode and a silicon bilateral voltage triggered switch. The switch becomes conductive upon the application of a substantial increase in voltage from the A.C. source and remains conductive until there is an interruption of the current flow or the current flow drops below its required holding value.
In a patent issued to H. J. Stier et al in Oct. 1957, U.S. Pat. No. 2,809,329, a "series lamp circuit with normal and stand-by lamps" is taught. In the Stier disclosure, a film cut-out is used as a by-pass switching device to shunt around a burned-out lamp. Film cut-outs are structured with an insulating plastic film placed in series between two conductors. When a lamp of the circuit burns out, the voltage of the circuit will rise sufficiently to burn through the plastic insulator to reestablish the circuit. It has been found that this type of by-pass switching device usually emits radio frequency waves while in the by-pass mode. The emitted radio waves cause static in nearby radios and thus the film cut-out switch is not a desireable switching unit. When the film is burned through by the electricity, insulator film is left around the burned hole through the insulating film. The insulating material around the hole prohibits a complete and solid contact between the conductors on each side of the film. Consequently, the current flowing through the switching unit in the by-pass mode will usually be flowing with a small degree of arcing between the two conductors of the by-pass switch. It is the arcing caused by the generally loose connection between the two conductors of the switching unit which creates the radio waves.
Of the past art devices and circuitry examined in the patent search which were designed to automatically by-pass a defective illuminant in a series circuit, several used either motors and electromagnets in combination with armatures, while others used solid state electronics, or burnt film cut-out switches to perform the switching. None of the known by-pass switches for series wired lighting appeared to be structured similar, or to function in the same manner as my by-pass switching device.